Materials for use for rainwear are known which have a layer of expanded microporous polytetrafluoroethylene (ePTFE) or porous polypropylene, see for example, Gore, et al., U.S. Pat. No. 4,194,041 or Henn, U.S. Pat. No. 4,969,998. Expanded microporous water-repellent polytetrafluoroethylene material described in Gore, U.S. Pat. No. 3,953,566 is especially well suited for this purpose. It is liquid water repelling, but allows water vapor, in the form of perspiration, to pass through. Polyurethanes and other polymers have been used for this purpose also. To confer good flexibility on the materials for use in the textile sector, the microporous layer should be made as thin as possible. However, a thinner membrane will generally mean a loss of performance, and thin coatings run the risk of decreasing water repellency.
U.S. Pat. No. 4,194,041 describes the use of an additional coating on microporous polymers which is based on a thin, air-impermeable coating composed of a polyetherpolyurethane or polyperfluorosulfonic acid that transports water vapor molecules by diffusion. The thin coating is employed to reduce transmission of surface active agents and contaminating substances through the polymers. Owing to the chemical structure of the polymer, the monolithic coating on the microporous structure exhibits a high transport of water molecules, (high permeability to water vapor) through the polymers material. This film should be applied as thinly as possible in order not to affect the flexibility, yet confer adequate protection on the composite. Furthermore, water vapor permeability deteriorates greatly in the case of thicker, monoithic films.
A type of composite membrane is known from U.S. Pat. No. 4,969,998. In this membrane the material of the inner layer has in part penetrated into the pores of the microporous outer layer. As the material for the microporous outer layer, microporous expanded polytetrafluoroethylene, is proposed. As for the inner layer a polyether-polythioether is proposed. The latter material up to a certain degree fills the pores of the microporcus layer, but is consistently tight, amorphous and nonporous. It is reported that this composite has moisture vapor transmission rates which are higher than the moisture vapor transmission rates of the laminate described first. However, when the composite was used as a textile laminate for rainwear it was found that under extreme athletic load and the associated heavy formation of perspiration, the latter cannot always be dissipated to the environment without residue. The liquid perspiration remaining on the inside of the clothing adversely affects the feeling of well-being and comfort of wearing.